Effect of apparent ileal digestible lysine to energy ratio on performance of growing pigs at different dietary metabolizable energy levels

The present study investigated whether the optimum ratio between dietary apparent deal digestible lysine and metabolizable energy (ME) in growing pigs is influenced by the energy density of the diet. Therefore, according to a bifactorial design, growing pigs were fed diets with 13.0 or 14.0 MJ ME/kg with ratios between apparent ileal digestible lysine and ME of 0.44, 0.53, 0.63 and 0.70 (g/MJ ME). Half the animals were barrows, half were gilts. The experiment was carried out throughout the body weight range between 28 and 58 kg. The parameters of animal performance assessed were body weight gain, feed intake, feed to gain ratio and energy to gain ratio. The feed intake of the animals was not influenced by the dietary treatment. The other parameters were markedly influenced by the ratio between apparent ileal digestible lysine and ME, but were independent of the energy density of the diet. The optimum ratio between apparent ileal digestible lysine and ME was nearly independent of the dietary energy level. According to exponential regression analysis, the optimum ratio was 0.66 g ileal digestible lysine/MJ ME for growth, regardless of the dietary energy density and at least 0.71 or at least 0.69 for optimum feed to gain ratio (at 13.0 and 14.0 MJ ME/kg, respectively). The ratio for optimum energy to gain was above the highest ratio used (0.71 g/MJ ME). Barrows exhibited higher feed intake (+11%) and body weight gain (+9%) than gilts. The optimum ratio between ileal digestible lysine and ME, however, was similar for gilts and barrows. In conclusion, the study shows that the optimum ratio between apparent ileal digestible lysine and ME is independent of the dietary energy level. The optimum ratio estimated was slightly above 0.70 g/MJ ME for pigs in a live weight range between 28 and 58 kg.